The present invention relates generally to cryomilled alloys and more particularly to cyromilled rhenium alloys.
The aerospace industry is increasingly becoming more competitive. To compete in the industry, it is necessary to develop propulsion systems that are low cost and can efficiently deliver high payloads. Rocket propulsion systems are commonly used for delivering payloads and spacecraft into space.
Many rocket propulsion systems use either a pressure fed system or a turbopump system that transfers propellants to the combustion chamber where they are mixed and burned to produce a high velocity stream of heated gases. The stream of heated gases is then exhausted through one or more nozzles to provide the desired thrust. Typically, combustion takes place at temperatures that may be in excess of 6000 F., which may be higher than the melting point of most conventional engine materials. As a result, in the absence of active cooling, it may be necessary to line the interior of the combustion chamber with a material having a high melting point and oxidation resistance.
Iridium-coated rhenium is a material that is commonly used to line the interior of the combustion chamber. Iridium provides high temperature oxidation resistance and has an intrinsic resistance to oxidation. Rhenium has a higher melting point than iridium and excellent high temperature structural capability. Iridium and rhenium are dense materials that are prohibitively expensive. As a result, the use of iridium and rhenium may increase the overall cost and weight of the propulsion system. Rhenium has also been advantageously used in solid rocket motor applications.
The processing of rhenium also presents several challenges. In many applications, chemical vapor deposition (CVD) fabrication is used. Typically, high temperatures are needed to deposit rhenium using CVD. However, conventional equipment for CVD produces temperatures on the order of 1000° C., which is much lower than the melting point of rhenium. CVD also typically requires relatively expensive starting materials and processing reactors that are relatively expensive to run and maintain. Other methods of processing rhenium, such as electrodeposition, may also present challenges and may result in the rhenium having an undesirable grain size. Post-processing, e.g. machining of rhenium, may also be difficult because of the high work hardening coefficient of rhenium.
The advantageous properties of rhenium may also be adversely affected, in part, by the processing conditions. For instance, in many cases rhenium properties may be dynamic when exposed to high temperatures. This dynamic behavior may result from grain growth that can occur at higher operating temperatures. Grain growth may decrease the mechanical properties of rhenium. Additionally, current methods of processing rhenium typically result in relatively large grain structures or grain structures that have an acicular grain structure. Such grain structures tend to increase the difficulty of processing rhenium and may also result in the rhenium having reduced mechanical properties, such as strength, at higher operating temperatures.
Thus, there still exists a need for a rhenium alloy and a method of processing rhenium that minimizes the level of rhenium that is required without decreasing the mechanical properties and high melt temperature of rhenium.